1. Field of the Invention
This invention relates generally to telephony, telephone equipment, and telecommunications systems, and more specifically to an improved telecommunications method and apparatus enabling the sharing of either or both POTS and ISDN signals with ADSL/VDSL signals on the same twisted pair copper channel medium.
2. Description of the Prior Art
Existing bidirectional telephony places the signalling for POTS (plain old telephone service) and ISDN (integrated services digital network) at baseband frequencies. For example, POTS baseband audio and signalling provides connectivity for conventional telephone services, and typically utilizes frequencies from approximately 0-4 kHz. Alternatively, ISDN channel requirements typically consume the 0-200 kHz frequency range.
ADSL (asymmetrical digital subscriber line) service, on the other hand, may utilize a frequency range of from 25 kHz to 1.1 mHz. Because these frequencies overlap ISDN frequencies (at least over the lower portion of the typical ADSL frequency range), it has been commonly held that one cannot combine ISDN and ADSL signals on the same twisted pair copper channel.
In addition, current telecommunication systems offering ADSL with POTS signals utilize passive audio combiners and splitters, which are physically large and bulky components, as well as being relatively expensive.
VDSL (very high-speed digital subscriber line) service is generally at higher frequencies, and thus avoids the overlap problem with typical ISDN frequencies. However, use of VDSL with POTS would still require the use of POTS splitters and/or passive filters.
The ADSL with RF POTS overlay of the present invention provides a method and apparatus for bidirectional telephony (i.e., POTS and/or ISDN) and utilizes RF technology to move the POTS or ISDN signalling away from the baseband frequency. The inventive method translates the initially baseband telephony signalling into one or more RF signals over twisted pair copper channels, in conjunction with an ADSL or VDSL signal on the same medium, and enables the flow of high information rate content in both directions.
Several alternative RF signals could be utilized, depending upon the particular application. For example, translation from the baseband frequency to narrow band FM signals may be preferable for many current telephone system installations, due to the superior signal to noise ratio that may be achieved with narrow band FM. Alternatively, other FM, AM, or even digital signalling could be utilized. Use of digital signalling could be particularly attractive in applications where digital equipment (such as existing ISDN equipment) is already in place.
The inventive method improves system performance, increases reliability, and reduces cost. The inventive method also eliminates the need for audio filters, and avoids echo and side tone line problems. In addition to the voice information, some or all of the functionality provided by existing loop current and ringing signals can be incorporated into the system. This provides the opportunity for the elimination of ringing transient problems, as well as for the conservation of electrical power.